The heart is a muscular organ that pumps blood continuously throughout the body. It is comprised of four chambers — the right and left atrium and the right and left ventricle.
The four chambers of the heart work together by alternately contracting and relaxing to pump blood throughout the heart. To accomplish this, the heart uses an electrical system to trigger a heartbeat. Essentially, the electrical system is the power source that makes all the heart's functions possible.
Blood vessels lead in and out of the chambers, which receive and distribute blood throughout the body. The four chambers of the heart are connected by four valves — the tricuspid, pulmonic, mitral and aortic valves. These valves work like one-way doors, allowing blood to flow in only one direction.
Blood Circulation
As the heart beats, it pumps blood through a system of blood vessels called the circulatory system. The blood that these vessels carry is essential for the body to function. Blood carries oxygen and nutrients to your body's tissues, assists in the removal of carbon dioxide and waste products and promotes the overall health of the body's tissues. There are three main types of vessels that make up this system:
- Arteries
- Veins
- Capillaries
How blood flow works
Blood enters the heart through two large veins, the inferior and superior vena cava, emptying into the right atrium. It flows from the right atrium through the tricuspid valve into the right ventricle. The right ventricle pumps blood to the pulmonic valve, and the blood flows into the pulmonary artery and to the lungs. Oxygenated blood returns from the lungs to the heart via the pulmonary vein into the left atrium. From the left atrium, blood flows through the mitral valve to the left ventricle. From the left ventricle blood leaves the heart through the aortic valve and flows into the aorta and to the body.
Coronary Arteries
The heart muscle needs its own supply of oxygen and nutrients to pump properly. Although its chambers are full of blood, the heart receives no nourishment from this blood. The heart receives its own supply of blood through a network of arteries of the body known as the coronary arteries.
Functions of right and left coronary arteries
The coronary arteries wrap around the surface of the heart. The two main coronary arteries, the right coronary artery and the left coronary artery, branch off from the aorta. The right coronary artery supplies the right atrium and right ventricle. It branches into the posterior descending artery. The left coronary artery branches into the circumflex artery and the left anterior descending artery. The left coronary artery supplies the left atrium and the left ventricle.
Narrow coronary arteries
Collateral circulation is a network of tiny blood vessels that usually remain inactive. When coronary arteries narrow to the point that blood flow to the heart is limited, collateral vessels become enlarged and active. This process allows for blood flow around the blocked artery to the heart muscle.
Our Cardiovascular Program continues to receive recognition as one of the top programs nationally. We are honored to provide high-quality, effective care for even the most high-risk patients.
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Check Out Our Heart and Vascular Program Awards and Recognition
The Froedtert & MCW health network has built a reputation for clinical excellence and our research draws patients from around the world. Our Heart & Vascular program recognitions include:
- Premier recognized Froedtert Hospital in 2025 as one of the nation’s 50 Top Cardiovascular Hospitals® according to its independent quality analysis based on a balanced scorecard. The hospitals recognized in the top 50 operated at lower cost and had better outcomes, recording significantly higher inpatient survival rates, fewer patients with complications, lower readmission rates and up to nearly $7,000 less in total costs per patient case. Froedtert Hospital was ranked in the category of top teaching hospitals with a cardiovascular residency program. No other hospital in Wisconsin was recognized with this national distinction.
- The International Cardio-Oncology Society (ICOS) recognizes our Cardio-Oncology Program as a gold level Cardio-Oncology Center of Excellence in 2025. ICOS certification is awarded to institutions and practices that demonstrate superior expertise in the care of patients who have heart disease, are at high risk or experience heart complications with cancer treatment. The ICOS awards bronze, silver and gold certification. Of the two ICOS-certified programs in Wisconsin, we are the only one that meets the stringent requirements needed to be recognized as a gold level Cardio-Oncology Center of Excellence.
- Healthgrades recognized Froedtert Hospital in its 2024 Specialty Excellence Awards, including one of America’s 50 Best Hospitals for Cardiac Surgery, one of America’s 100 Best Hospitals for Cardiac Care and one of America’s 100 Best Hospitals for Coronary Intervention, as well as other specialty achievements in various areas.
- Becker’s Hospital Review recognized Froedtert Hospital within its 2024 list of 100 Hospitals and Health Systems with Great Heart Programs. Hospitals featured on this list are renowned for delivering superior heart and vascular care that results in high-quality outcomes. As part of a health network that includes eastern Wisconsin’s only academic medical center, our heart and vascular specialists treat a high volume of patients with a wide variety of heart diseases.
- Froedtert Hospital is recognized as a Surgical Quality Partner and Verified Comprehensive Inpatient Vascular Center by the American College of Surgeons Vascular Verification Program. As the first hospital in Wisconsin to receive this designation, this recognition, shows our commitment to our patients in delivering the highest standards in surgical care. Learn more about this recognition.
- The Society for Vascular Surgery's Vascular Quality Initiative (SVS VQI) recognized Froedert Hospital as a Carotid Care Quality Champion by the SVS VQI‘s clinical registry recognition program in 2024. The VQI recognizes select centers across the country as Carotid Care Quality Champions for their dedication to improving the safety and effectiveness of vascular care through participation and engagement in VQI’s carotid artery stenting and/or carotid endarterectomy registries.
- The American Heart Association recognized Froedtert Hospital with the following awards that show our commitment to improving care by adhering to the latest treatment guidelines and streamlining processes to ensure timely and proper care for heart attacks.
- Get With the Guidelines® Heart Failure Gold Plus Award
- Get With the Guidelines® — Coronary Artery Disease STEMI Receiving Gold Plus with Target: Type 2 Diabetes
- Get With the Guidelines® — Coronary Artery Disease NSTEMI Gold with Target: Type 2 Diabetes
- Get With the Guidelines® AFib Gold Award
- Get With the Guidelines® — Resuscitation Target CPR; Resuscitation Gold — Audit; Resuscitation Target Survival
- Froedtert Hospital earned the American Heart Association (AHA) Commitment to Quality award, a new AHA recognition, in 2025. The award recognizes adherence to the latest, research-based clinical guidelines to support better outcomes for patients.
- In addition, the hospital was recognized on the American Heart Association’s Target: Heart Failure(SM) Honor Roll and received the AHA’s Target: Type 2 Diabetes Honor Roll™ award.
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